Actually, you can JOIN two HOLD files, but there are certain rules and restrictions. These are a result of HOW we do the JOIN with sequential files. We NEVER back up. As a result, the 2 rules are:
1. Both files must be sorted in ascending order, on the common field (used for the JOIN).
2. There can be duplicate values in only ONE of the files. If in the host, the you should use a JOIN ... TO ...; if in the target use JOIN ... TO ALL .... If there are duplicates in both files (which would require us to back up to correctly process, then use the HOLD FORMAT FOCUS INDEX syntax on the target file, so the above rules no longer apply.